1. Field of the Invention
The invention relates to the field of contraception and to the subfields of human female contraceptives and oral contraceptive devices.
2. Description of the Prior Art
The physiological processes occurring during the menstrual cycle of the woman are regulated by hormones from at least (1) the hypothalamus, (2) the hypophysis and (3) the ovary. In the first phase of the cycle, the follicular phase, the gonadotropic hormone FSH (Follicle Stimulating Hormone) is secreted by the hypophysis. FSH effects the development and maturation of one or more follicles in the ovary. In addition, oestrogen production increases, and under the oestrogenic influence, proliferation of the endometrium occurs.
In a second phase, follicle maturation is followed, about halfway through the cycle, by ovulation ond development of the corpus luteum from the ruptured follicle under an influence of another gonadotropic hormone, LH (Luteinizing Hormone). The secretion of the LH hormone is regulated by the hypothalamus, which in turn is again subject to ovarian influence.
Similarly under hormonal influence, the corpus luteum secretes progesterone during the luteal phase which follows ovulation; progesterone ensures that the proliferative endometrium changes into a secretory endometrium, suitable for implantation of a fertilized ovum. If the ovum is not fertilized during its journey through the Fallopian tubes to the uterus, the corpus lutenum disappears after about 10 days, the progesterone level falls, and the endometrium is sloughed (menstruation).
Based on this hormonal process, a first generation (and now "classical") contraceptive method was developed about a decade ago based on the daily administration of a combination of (1) suitable oestrogenic and (2) suitable progestagenic substances over a period of a large fraction (usually 20 to 22 days) of the menstrual cycle. As a result of this so-called "combined treatment", ovulation is suppressed and an artificial monthly anovulatory bleeding is provoked.
This method is in general fairly reliable to prevent ovulation, but in addition to a number of unwanted incidental side effects such as nausea and weight increase, the method possesses a disadvantage that it brings about a deviation from the normal hormonal pattern.
A second method of contraception, developed at a later date, is the "continuous luteal supplementation" method, in which a suitable progestagenic substance is administered daily in low dosage throughout the entire cycle, and in the absence of an oestrogenic component.
The dosage used in this method is such that complete suppression of hypothalamic and hypophyseal function does not occur, so that the endogenous production of oestrogen is maintained, and inhibition of ovulation occurs sometimes, but often does not occur. In this method, the contraceptive properties are due to inhibition of the cyclical changes in the cervical mucus, as a result of which blockade of spermatozoa migration and inhibition of endometrial development occur. One of the major disadvantages of the continuous luteal supplementation method is that the constant administration of a progestagenic substance permits only a poor development of the endometrium, as a result of which irregular bleedings occur with all the associated objections.
It has already been suggested that these objections (nausea, weight increase, and irregular bleedings, inter alia) can be met by administering only a progestagenic substance, not throughout the entire cycle, but only for ten to fourteen days, beginning on day eight through ten of the cycle (see British patent specification No. 1,304,239), though in a dosage somewhat higher than that which is usual in the "continuous luteal supplementation" method, for example, 0.5-0.75 mg chlormadinone acetate. The change of inhibition of ovulation then increases, but the risk that ovulation occurs after ceasing administration also increases, so that contraceptive protection is then absent. For an example of another method, see U.S. Pat. No. 3,502,772 (1970).
An effective contraceptive method was needed, together with a suitably packaged pack with easily-administered components therefor which would prevent a deviation from the normal hormonal pattern while at the same time avoiding nausea, weight increase, and irregular bleedings, etc.